FDA approval of ipilmumab (anti-CTLA-4 antibody) and Provenge (dendritic cell vaccine for prostate cancer) as well as exciting recent results from clinical trials that assessed adoptive cell therapy (ACT) or checkpoint blockade, suggest that immunotherapy may one day replace radiation and chemotherapy as the primary intervention for cancer. Despite these promising results, however, fundamental questions must be answered before these approaches can become dependable, universal frontline therapies. For example, the efficacy of ACT may be restricted by the limited survival of the transferred T cells, as a diret correlation between their longevity and their clinical efficacy has been observed in clinical trial, suggesting the need for long-lived T cells for optimal outcomes. However, extending the lifespan of the genetically modified, transferred T cells complicates the manufacturing process, and might also result in unanticipated toxicities. In this exploratory study, we will determine the actual length of time that transferred T cells must persist for ACT to be clinically effective, and additionally will test whether enhancing endogenous T cell responses with anti CTLA-4 and/or anti-PD-1 therapy can augment overall ACT efficacy, minimizing the need for their prolonged lifespan. Although systemic interventions aimed at inducing potent anti-tumor T cell-mediated responses have mostly failed, recent trials demonstrated that blocking immunological checkpoints can enhance the anti-tumor activities of endogenous T cells, rendering them at least partially therapeutically effective. Given the significant but incomplete anti-tumor responses individually mediated by ACT and checkpoint blockage of endogenous T cells, we now have an unprecedented opportunity to determine whether the two distinct interventions can synergize to further improve responsiveness, potentially offsetting the need for long-lived and potentially toxic genetically modified T cells. Our laboratory is uniquely poised to perform these studies, given our murine model for ACT that will allow the targeted depletion of either endogenous or transferred CD8 T cell populations. This highly innovative approach will be used to: 1)establish the relative contributions of endogenous and transferred T cells to a curative anti tumor memory response, and 1) determine whether augmenting the effector function of host T cells using systemic immune enhancing drugs during initial tumor regression mediated by ACT overcomes the need for an extended persistence of transferred T cells. These results will be important in the design of immunotherapeutic approaches that combine ACT and checkpoint blockade, which can extend their applicability to other malignancies.